Protection of metallic surfaces



Patented Dec. 15, 1936 UNETEE STATES PATENT GFFECE Hubert Sutton and Laurence Francis Le Brocq, South Farnborough, England No Drawing. Application December 18, 1935, Serial No. 55,066. In Great Britain December 2 Claims.

This invention relates to a method of and means for protecting metallic surfaces from corrosion or deterioration when in contact with organic liquids such as liquid hydrocarbons, e. g.

5 petrol, paraffin, or lubricating oil, alcohols, or

vegetable or animal oils.

The invention has particular reference to cases Where it is is desired to store liquid hydrocarbons or alcohols for use as fuels or lubricants for internal combustion engines, in metal containers and for the sake of simplicity the invention will hereinafter be described in its application to this purpose.

It is known that metal containers in which liquid hydrocarbons are being stored suffer considerably from corrosion which may give rise to perforations and to leakage. This corrosive effeet is particularly marked in the case of containers constructed of high-grade magnesium alloys and to a somewhat lesser extent in the case of those constructed of aluminium or its alloys.

Although the reason for such corrosion is not apparent, it may be due to the presence in the hydrocarbon of free water which need not necessarily be introduced into the containers as such, but-may be precipitated from solution in the hydrocarbon by temperature changes or changes in the composition of the hydrocarbon.

Thus, fuel for internal combustion engines if carefully dried, may be stored indefinitely in magnesium alloy containers but if it contains free water, corrosion occurs on various parts of the container. Corrosion is greatly increased if the fuel contains anti-knock substances such as mixtures of lead tetra-ethyl and ethylene dibromide.

The present invention aims at preventing or minimizing such corrosion or deterioration of metallic surfaces when in contact with organic liquids of the kind hereinbefore set forth.

To this end, according to the invention, a salt of chromic acid soluble or sparingly soluble in water is introduced into the organic liquid.

Examples of the salts of chromic acid which may be employed when carrying out the invention are, for example, sodium chromate or dichromate, potassium chromate or dichromate and magnesium chromate or dichromate, but preferably only sparingly soluble in water salts such as strontium chromate, calcium chromate, basic calcium chromate or zinc chromate are employed.

Preferably the salt of chromic acid is introduced into the liquid hydrocarbons in bulk or agglomerated form and not in the form of discrete particles. Thus for example, in carrying out the invention the salt of chromic acid may be enclosed in a small fabric bag or reticulated structure and the package may be introduced into the container for the hydrocarbon.

The corrosion inhibiting substance may be introduced at one or more positions in the container, for example at the bottom, if corrosion is more likely to take place at that part.

For this reason, the use of slightly soluble chromates is to be preferred as the contents of the bag are only slowly brought into use and due to the low concentration thereof in solution recrystallization of the chromates due to temperature changes is comparatively unobjectionable.

It is however not necessary to confine the corrosion inhibiting salt in a fabric bag, but it may be mixed in the form of powder with an agglutinating agent and if desired, a solution retarding agent, such as starch, and compressed into the form of pastilles, rods, tablets or the like, which may be disposed in any convenient manner in the container to be protected.

For many purposes a solution of cellulose nitrate in a mixture of benzol and alcohol with or without plasticizers may be used as an agglutinating agent.

However any other known agglutinants or binders which do not enter into harmful reaction with the corrosion inhibiting salt may also be used such as for example casein, synthetic resins, Portland cement or sodium silicate.

Again, instead of mixing the corrosion inhibiting salt with an agglutinating agent it may be fused, if capable of fusion without detriment to its corrosion inhibiting properties, and cast into rods, blocks or the like, or it may be powdered and then compressed into tablets or other convenient form.

The effects of the hereindescribed process are particularly marked in the case of magnesium alloys as will be evident from the following comparative test:-

A tank constructed of 18-gauge magnesium base alloy (Air Ministry Specification No. DTD 118) was filled with high-grade petrol (Air Ministry Specification No. DTD 230) containing 7 cc. of ethyl fluid (lead tetra-ethyl plus ethylene dibromide) per gallon. This tank became perforated due to corrosion within 95 days.

A similar tank containing the same petrol mixture in which was suspended a bag containing potassium chromate remained unaffected by corrosion after twelve months.

The invention is not confined to the protection of storage vessels but is equally applicable to the protection of metallic or other parts of mechanical systems which come into contact with organic liquids such as pipes, carburetters, filters, crank cases, oil pumps and the like.

Thus, as example, parts of fuel systems for aircraft are fitted with a perforated metal cage located at the lowest parts of the fuel system. In this cage a small bag containing calcium chromate may advantageously be placed and may be renewed from time to time.

Similarly, a small tablet or pellet of a waterso-luble chromate or di-chromate may be placed in the petrol filter or carburetter of aircraft or motor car engines. I

Although the invention has hereinbe'fore been more particularly described in connection with the prevention of corrosion by hydrocarbons, it should be understood that it is equally useful for preventing corrosion by alcohols, such as methanol and ethanol, particularly when used as fuels for internal combustion engines and also for the prevention of corrosion by vegetable and animal oils such as castor oil and whale oil respectively,

in which latter case the chromates when used would also serve to inhibit or reduce the rancidity of the oil.

We claim:

1. The method of protecting a surface of a container made of corrodible metal selected from the group consisting of magnesium, aluminum and alloys thereof against the corrosive effects of fuels and lubricants comprising liquid hydrocarbon comprising inserting into said container a preformed body comprising a chromic acid salt, so as to maintain contact between said salt and the liquid hydrocarbon containing substance.

2. The method of protecting a surface of a container made of corrodible metal selected from the group consisting of magnesium, alluminum and alloys thereof against the corrosive effects of fuels and lubricants comprising liquid hydrocarbon comprising inserting into said container a preformed body comprising a chromic acid salt and a binder therefor, so as to maintain contact between said salt and the liquid hydrocarbon containing substance.

HUBERT SUTTON. LAURENCE FRANCIS LE BROCQ. 

